1. Field of the Invention
The present invention relates to a surface acoustic wave device suitably employed for a filter element, a duplexer, and so forth and carrying a plurality of surface acoustic wave elements respectively having different frequency pass bands, and a communication apparatus comprising the surface acoustic wave device. The communication apparatus is employed for a mobile communication apparatus such as a cellular phone, for example.
2. Description of Related Art
In a communication apparatus such as a cellular phone, a surface acoustic wave device using a surface acoustic wave element comprising an IDT (Inter Digital Transducer) electrode as a duplexer for separating a transmission signal and a receiving signal. The surface acoustic wave device is a small in size, has steep filter element characteristics, and has superior properties such as superior mass productivity.
Particularly in recent years, a small-sized surface acoustic wave device having a transmitting filter element and a receiving filter element integrated with each other is required in the surface acoustic wave device in order to make the communication apparatus small in size and lightweight. Although it goes without saying that low insertion loss is required as the filter element, a larger attenuation is required for out-of-band attenuation characteristics.
If the respective out-of-band attenuation characteristics of the transmitting filter element and the receiving filter element are degraded, an unnecessary radio signal is transmitted or received, thereby causing the possibilities that the quality of the received radio signal is degraded, and there arise problems such as interference with another radio communication apparatus.
The out-of-band attenuation characteristics of the conventional surface acoustic wave device cannot sufficiently cope with the foregoing requirements. A further improvement is desired.
The present invention has been devised in view of the foregoing desires, and has for its object to provide a surface acoustic wave device that comprises a high-frequency side filter element and a low-frequency side filter element, is superior in out-of-band attenuation characteristics of the filter elements, can be miniaturized, and is high in reliability.